Antibodies Against Cells of Fetal Origin

ABSTRACT

This invention relates to antibodies that specific bind to fetal CD36+ cells in preference to binding to maternal CD36+ cells and methods for using these antibodies to detect and separate fetal cells from adult biological fluids including maternal peripheral blood.

This application claims priority to U.S. Ser. No. 60/579,693, filed Jun.14, 2004 and U.S. Ser. No. 60/618,963, filed Oct. 15, 2004, theteachings of each of which are explicitly incorporated by referenceherein.

FIELD OF THE INVENTION

This invention relates to antibodies that bind to fetal CD36+ cells inpreference to binding maternal CD36+ cells and the use of theseantibodies for detecting and separating fetal cells from maternalperipheral blood.

DESCRIPTION OF RELATED ART

The presence of fetal red blood cells in maternal blood immediatelyafter delivery was first reported by Zipursky et al. in 1959 (“Foetalerythrocytes in the maternal circulation,” Lancet 1:451-52). It wassubsequently demonstrated that fetal red cells, lymphocytes andtrophoblasts cells are present in maternal blood during pregnancy.(Herzenberg et al, 1979, Proc Natl Acad Sci USA. 76: 1453-1455; Bianchiet al., 1990, Proc Natl Acad Sci USA. 87:3279-83) It has been widelyrecognized that the presence of fetal cells in maternal blood providesan opportunity to obtain fetal cell samples for clinical diagnostictesting and for research purposes at minimum risk to the fetus. Thiscontrasts to currently widely used methods of obtaining fetal cellsamples such as chorionic villus sampling (CVS), amniocentesis, orperiumbilical blood sampling (PUBS). While effective and widely used,these methods are directly invasive to the fetus and can increase riskof fetal morbidity or mortality, including miscarriage. The usefulnessof obtaining fetal cells from maternal blood is, however, limited by thelow numbers of fetal cells that are present in the peripheral blood ofthe mother. The reported ratios of fetal to maternal erythroid cells aregenerally in the range of 1:4,000 to 1:80,000. The correspondingreported ratios for lymphocytes are considerably more variable, rangingfrom 1:100 to 1:300,000 depending upon multiple factors including thespecific analytical method used and the gestational age of the fetus.

Numerous methods for recovering fetal cells from maternal blood havebeen proposed. One group of such methods, exemplified by U.S. Pat. No.5,641,628 and incorporated herein by reference, proposes using fetalcell-specific monoclonal antibodies, particularly anti-CD71 (transferrinreceptor) to bind to fetal erythroid cells. Others have employedantibodies specific for cell surface antigens such as CD34 andglycophorin A for similar purposes. Certain commonly practicedembodiments of this approach employ antibodies that have been conjugatedto a detectable moiety such as a fluorophore. Conjugated antibodybinding to a fetal cell permits these cells to be detected in thepresence of other cells that do not display the cognate antigen. Thisdetection is sometimes used in conjunction with fluorescence activatedcell sorting (FACS) instrumentation to permit labeled fetal cells to beseparated from the commingled unlabeled maternal cells. In other commonembodiments of this approach, fetal cell-specific antibodies areattached to a solid surface or magnetic microparticle and use theimmobilized antibody to capture fetal cells. Antibody binding to thetarget fetal cells attaches them to a supporting surface, microparticle,microporous filter, porous insoluble matrix or other such entity whilethe maternal cells are not bound and will, therefore, remain in theliquid phase. The supporting entity with bound fetal cells can then bereadily separated from the maternal cell-containing liquid phase. Bothclasses of fetal cell-separating methods are based upon and utilizeaccepted methods and materials that are well established in the art forthis and other related purposes. These approaches are limited by theaforementioned rarity of fetal cells in maternal blood, as well as thedevelopmental biology of hematopoietic and fetal stem cells.

Detecting fetal cells in maternal blood using the methods describedabove is an exercise in “rare event” detection. Performance of thesedirect immunological methods is difficult to accurately assess from mostpublished data because, inter alia, typical metrics are reported as the“yield of pure product” or “sensitivity” and “specificity”; or the datato compute such metrics are frequently not reported at all. It is morecommon for labeled or, if appropriate, recovered cell counts to bereported without further determination or reporting of either falsenegatives or false positives contained therein. Crude estimates ofperformance, however, can be derived based upon the total cell count inthe sample and an estimated frequency of occurrence of the cell type(s)of interest in the sample. By way of example, assuming that it isreported that a sample contains 1×10⁷ total cells and that the frequencyof occurrence of the target cells in the sample is 1:25,000 (both valuesbeing realistic for experiments in which fetal erythroid cells arelabeled in or recovered from maternal blood), it can reasonably beanticipated that there will be approximately 40 fetal cells in thesample. If the reported number of cells that are labeled or recoveredusing the method being described is substantially less than thisanticipated value, the sensitivity of the method, i.e., the ratio orpercentage of the fetal cells actually present in a sample that aredetected by the method, can be considered low. Conversely, if thereported number of cells that are labeled or recovered using thedescribed method is substantially greater than this anticipated value,the specificity of the method, i.e., the ratio or percentage of thecells detected by the method that are actually fetal cells, is low.Applying this type of meta-analysis to published experimental resultsfor the labeling or recovery of erythroid fetal cells from maternalblood often yields an imputed value of sensitivity or specificity (asappropriate) of less than 25% and occasionally less than 10%.

These imputed sensitivities and specificities for direct immunologicallabeling or capture of fetal cells can be put into perspective byconsidering the results reported for the closely analogous applicationof immunochemical screening of cervical cytology specimens for thepresence of dysplastic and cancerous cells. Like fetal cell detection,cervical cytology screening is an exercise in rare event detection inwhich the frequency of occurrence of cells of interest is often in the1:10,000 to 1:50,000 range. Similarly, some of the same antibodies, mostnotably an antibody specific for CD71, are used in some implementationsof both applications. The methods employed in performing the labeling ofthe sample, for capturing the data; and interpreting these results islikewise very similar. Sensitivities and specificities are, however,routinely reported for the cervical cytology results typically fallwithin the 85% to 95% range. This comparison strongly suggests that boththe sensitivity and specificity of methods for direct immunologicallabeling or capture of fetal cells in or from a sample of maternal bloodis inadequate.

Numerous attempts have been made to improve the sensitivity andspecificity of fetal cell labeling and/or recovery from maternal blood.These improvements have taken the form of enriching the specimen infetal cells prior to performing the final labeling or capture steps.Virtually all practitioners of this art, for example, sediment thematernal blood sample through a Ficoll or similar density gradientbefore performing any operations that are fetal cell-specific. Thissedimentation process permits a maternal blood specimen to be separatedinto three major fractions: erythrocytes, mononuclear cells andplatelets. The erythrocyte and platelet fractions together account forthe vast majority of the cells present in the original sample, while themononuclear fraction contains the fetal cells of interest. Removing thebulk of the potentially interfering cells from the samplenon-specifically enriches for target fetal cells and improves thelikelihood that these cells will be labeled or captured. However, mostcurrent separation methods, including the ones discussed in thepreceding paragraph, employ such enrichment methods, indicating thatenrichment is not sufficient to remedy the deficiencies in specificityand sensitivity known in these prior art methods.

Consequently, the mononuclear fraction has been further enriched by someworkers. One commonly-employed method (see, for example, U.S. Pat. No.5,641,628) selectively isolates cells from the monocyte fraction thatdisplay cell surface antigens associated with fetal cells. Conversely,cells that do not display fetal cell-associated antigens can be removed(subtracted) from the mixture (this is illustrated in U.S. Pat. No.5,877,299). Such selective isolation of fetal cells typically usesantibodies specific for early stage fetal cell markers such as CD34and/or CD133, used either alone or in combination. The subtractiveapproach typically uses “cocktails” containing multiple antibodies, eachof which is specific for a particular type of cell to be removed fromthe mixture. The mechanics of such separations are generally asdescribed above and are based upon established methods such as FACS,magnetic separation, affinity chromatography or cell panning.

The primary limitation on the efficacy of this approach is a consequenceof the process of cell development. All cells derive from pluripotentstem cells that have the potential to differentiate to form virtuallyany cell that is found in an organism. Pluripotent stem cells are thepredominant cell type in very early stage embryos, but decline rapidlyin number to the point of undetectability as the embryo develops. Duringdevelopment the ability of these pluripotent stem cells to differentiateis progressively reduced as these cells become committed to theformation of specific organs and tissues. The initial restriction ondifferentiation results in the formation of classes of multi-potent stemcells, each class being capable of giving rise to all cell types withina particular broad range. Hematopoietic stem cells, for example, cangive rise to any of the blood cell types. These stem cells haveconsiderable proliferative potential and exhibit the properties ofself-renewal, engraftment and, when appropriately stimulated,differentiation into “progenitor” stem cells. These progenitor cellsretain the proliferative and engraftment capacities of the parentmultipotent stem cells, but are restricted to differentiation into cellsof a specific hematopoietic lineage. Whereas, for example, hematopoieticstem cells can give rise to cells of the erythroid, myeloid,megakaryocytic, lymphoid, and, possibly, veto lineages of blood cells, aprogenitor cell derived from a hematopoietic stem cell is committed todifferentiating into the cells of just one of these lineages (i.e.,erythroid, myeloid, megakaryocytic, etc.). Like pluripotent andmulti-potent stem cells, progenitor cells are not distinguishable on thebasis of morphology, but rather are recognized by their progeny. Whensuitably stimulated, these progenitor cells undergo additional rounds ofdifferentiation leading to the penultimate differentiated cell withinthe particular progression. Within the erythroid lineage, for example,an early stage of differentiation presents as a “burst formingunit-erythroid” (BFU-E) and later presents as a “colony formingunit-erythroid” (CFU-E) before progressing to the morphologicallyidentifiable erythroblast “precursor” cells. These precursor cellsfurther progressively differentiate through the proerythroblast,basophilic, polychromatophilic, and orthochromatic erythroblasts stagesbefore enucleating to become reticulocytes and ultimately erythrocytes.

This progression of changes resulting from differentiation is reflectedin changes in the cell surface antigens that are presented by the cell.Within the erythroid progression, for example, hematopoietic stem cellsand BFU-E cells express CD34 and 17F11 (c-kit) while CD33 is expressedduring the BFU-E stage, but none of these antigens are expressed duringthe CFU-E or later stages. CD71 (transferrin receptor, TFR) appears inthe late BFU-E or early CFU-E stage and persists through thereticulocyte stage, while CD36 (thrombospondin receptor, TSPR) appearslate in the CFU-E stage and persists even in some mature erythrocytes.Glycophorin A and the Blood Group A antigen appear at the erythroblaststage and persist into mature erythrocytes. Other antigens show similarchanges in expression as a function of the stage of differentiation.

This variability in expression is one limitation on using these antigensfor separating fetal cells from non-fetal cells. Using CD34, forexample, identifies cells at the hematopoietic stem cell and BFU-Estages, but does not identify any of the later progeny. Conversely, CD71does not identify cells at the hematopoietic stem cell and BFU-E stages,but does identify later stage cells. Thus a combination of CD34 and CD71antibodies would need to be employed in order to ensure that all of thecells of interest are labeled and/or captured in order to avoid asignificant loss in sensitivity. A similar situation applies to“subtractive” methods of sample enrichment because they requireantibodies that bind to all of the undesired cell types in all of theirdevelopmental stages without binding to fetal cells.

A further limitation on existing methods of fetal cell separation isthat many of these antigens appear on multiple, often unrelated celltypes. CD71, for example, is intimately involved in iron metabolism andis therefore expressed by virtually all actively respiring mammaliancells. Similarly, CD36 is involved in cell adhesion and certainregulatory functions and is expressed by a variety of blood and othercell types. This expression of antigens across broad ranges of celltypes impairs the specificity of methods dependent on these antigens. Inaddition, expression of certain of these cell surface markers isdependent not only on cell type and developmental stage but on a varietyof other, environmental factors that reduce the usefulness of theseantigens as differentiation markers. CD71, for example, is under tighttranscriptional, translational and post-translational regulation.Expression of CD71 is controlled not only by the stage of development ofthe cell, but also by numerous environmental factors. This environmentalsensitivity can reduce the method's, sensitivity, specificity or both.Finally, fetal and maternal blood cells of the same type and developmentstage express essentially the same antigens, making it difficult todistinguish the origin of any particular cell. Under certaincircumstances, this type of limitation can be overcome: fetalerythroblasts express fetal hemoglobin while the maternal erythroblastsexpress the adult form, for example, and the paternal Y chromosome canbe detected in cells from male fetuses.

In light of these limitations, other methods have been developed forselectively enriching the fetal cell component of maternal bloodsamples. One approach, disclosed in U.S. Pat. No. 5,580,724, uses thehigher proliferative capability of fetal cells compared with maternalcells of the same cell type. In this method, CD34⁺ cells are collectedfrom the maternal blood sample in accordance with one of the methodsoutlined above and then expanded in cell culture in the presence of theappropriate cytokines and other factors. As fetal CD34⁺ cells have ahigher proliferative capability than do maternal CD34⁺ cells, expansionthrough multiple cycles of cell division progressively increases theproportion of early stage fetal cells in the culture. As the combinationof cytokines and other factors used to promote this selective expansionare largely specific for the promotion of proliferation but notdifferentiation of CD34⁺ cells, the population of later stage fetalcells is not expanded to a similar degree.

U.S. Pat. No. 5,843,633 discloses yet another approach, in which intactfetal cells or stem cells are used as immunogens for preparingmonoclonal antibodies. This method results in a complex mixture ofhybridomas each of which expresses an antibody that is directed againstone of the panoply of antigenic epitopes that are displayed by fetal orstem cells. These hybridomas are typically purified into clones eachexpressing a single antibody that is then individually screened againstpanels of fetal and other cell types to determine which, if any, ofthese antibodies exhibits useful levels of specificity for fetal cells.In order to adequately assess antibody specificity, the screening panelsmust include pure specimens of the target fetal or stem cell type(s) aswell as specimens of all of contaminating cell types that may be presentin a clinical sample. Hybridomas of sufficient specification are thenexpanded to produce larger quantities of the selected antibody. Whilesuch methods have the potential to have sufficient specificity, they arelimited by the exhaustive screening that is required in order toidentify antibodies exhibiting adequate specificity for fetal or stemcells.

Additional fetal cell-specific antigens have been discovered bycomparing proteins or genes expressed by fetal cells proteins or genesexpressed by maternal cells to identify those proteins or genes that arestrongly expressed in fetal cells, but not in maternal cells. Thequality of the comparisons obtained by this method is sensitive to thepurities of the maternal and fetal cells used as specimens and to thestringent procedural control required in order to obtain reproducibleresults. These experiments have been performed using various microarrayshaving signal-to-noise ratios sufficiently low that significant numbersof replicates must be run in order to obtain useful results. The geneticdiversity of each sample and the “coverage” of the array in terms of thepercentage of the total possible number of targets actually representedin the array are also significant considerations. A particularlimitation is that the maternal and fetal cells of interest for thepresent purpose are primarily stem cells and cells at the BFU and CFUstages of differentiation. These cells are not recognizable bymorphological criteria, but rather are recognized only through theirprogeny. This introduces significant uncertainty as to the identities ofthe cells used in this procedure. In any case, once the antigen(s) thatis/are uniquely expressed by fetal cells is/are identified, thecorresponding proteins can be obtained and antibodies raised againstthese proteins in accordance with standard methods.

There thus remains in the art a need for more specific and sensitivemethods for identifying markers that can distinguish fetal cells frommaternal cells, markers useful in such methods, and reagentsparticularly antibodies for detecting such markers.

SUMMARY OF THE INVENTION

The present invention provides antibodies that preferentially bind tofetal cells rather than maternal cells, methods for preparing suchantibodies and methods for using these antibodies to detect and separatefetal cells from other cell types. A particular and advantageousapplication of the methods and antibodies of this invention is tospecifically label fetal cells and separate such cells from other celltypes, particularly maternal cells. Fetal cells isolated using theinventive antibodies and methods are useful for fetal genetic analysisfor detecting or diagnosing disease states or for determining fetalgender, and may find further utility in cell-based therapies.

The present invention advantageously differs from existing methods for

labeling or capturing fetal cells from maternal blood because, interalia, it forces fetal cells present in a sample into a pre-defined stateprior to labeling or capture, thus allowing the entire population offetal cells that is present to be labeled or captured by the antibodiesof the invention. By way of example, antibodies against cellsurface-specific antigens CD34 and CD133 that are widely used separatelyor in combination predominantly label or capture erythroid fetal cellsthat are at the CFU-E or earlier stage of differentiation, but do notlabel or capture erythroid fetal cells at later stages ofdifferentiation. This reduces the yield of fetal cells that can beobtained from a maternal peripheral blood sample. Furthermore, thisyield depends upon the degree of differentiation that has happened tooccur in the fetal cells in the sample. Forcing all of the fetal cellsinto a pre-defined state and employing antibodies that are specific forunique antigens that are expressed by fetal cells in this state permitsa higher percentage of the fetal cells in a sample to be labeled orcaptured in a consistent manner.

The methods of the invention are also advantageous because they permitfetal cell samples to be obtained using minimally invasive methodswithout posing risks to the fetus.

Specific preferred embodiments of the invention will become evident fromthe following more detailed description of certain preferred embodimentsand the claims.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows a schematic flow chart for the preparation of fetal cellspecific antibodies

FIG. 2 shows a schematic flow chart for the use of fetal cell antibodiesin the separation of fetal cells from maternal peripheral blood.

DETAILED DESCRIPTION OF THE INVENTION

Antibodies provided according to this invention were prepared againstpeptide antigens that were chosen based upon a systematic investigationof differences in gene expression between fetal and maternal cells whensaid cells are forced into a pre-defined state. The samples employed inthese investigations consisted of separate pools of CD34⁺ cells(hematopoietic stem cells and erythroid progenitor cells) of fetal andmaternal origin. These pools of cells were separately expanded in thepresence of the appropriate cytokines and other factors to increase thenumbers of CD34⁺ cells present in the pools. These expanded pools ofCD34⁺ cells were then separately expanded in the presence of certaincytokines and other factors that promote the differentiation of theCD34⁺ cells to form cells that express CD36, but not CD34.

The total RNA from these pools of fetal and mobilized adult CD36⁺ cellsorigin was then separately extracted and transcribed into thecorresponding cDNA preparations that were, in turn, hybridized to“expression” or “EST” microarrays from which the genes or ESTs that areuniquely expressed by CD36⁺ cells of fetal origin can be determined. Theamino acid sequences of the proteins that were encoded by these uniquelyexpressed fetal genes were then determined and evaluated to identifyshorter sequences of amino acid residues (typically 10-30 residues) thatare unique to the fetal proteins and were not found in any of the geneproducts (proteins) expressed by CD36+ cells of maternal origin underthe same conditions. These unique fetal peptides were synthesized;conjugated (if necessary or advantageous for antigenicity) to a carriersuch as Keyhole Limpet Hemocyanin; and used as immunogens for preparingmonoclonal or polyclonal antibodies that bind specifically to theseunique fetal peptides. These fetal-specific antibodies were thenconjugated to a detectable label such as a fluorophore or immobilized onan insoluble support such as a magnetic microparticle, depending uponwhether the antibody is to be used for labeling fetal cells or capturingfetal cells from maternal peripheral blood samples.

The antibodies of the present invention can be used to recover erythroidcells of fetal origin from samples of maternal peripheral blood, andthus the invention provides methods therefor. In these methods of theinvention, the CD34⁺ cell fraction is isolated from maternal peripheralblood in accordance with conventional blood cell separation methods andexpanded in the presence of the appropriate cytokines and other factorsto force differentiation of the CD34⁺ cells into cells that express CD36rather than CD34. If the resulting CD36+ cells are to be identified inthe sample, for example, by fluorescence microscopy or are to beseparated from the sample, for example, by fluorescence-activated cellsorting (FACS), the sample is treated with one or more of the antibodiesof this invention that have been conjugated to a detectable label suchas a fluorophore. If the resulting CD36+ cells are to be directlycaptured from the sample, for example, by magnetic separation, cellpanning or affinity chromatography, the sample is treated with one ormore of the antibodies of this invention that have been immobilized onan insoluble support of a type that is appropriate to the intendedseparation method.

Cells that have been labeled as set forth in the preceding paragraph canbe evaluated microscopically or further analyzed for fetal gender,genetic abnormalities and disease states by in-situ methods such asfluorescence in-situ hybridization (FISH) or reacted with otherantibodies or probes and analyzed by flow cytometry. Cells that havebeen captured in accordance with the methods of the preceding paragraphcan be further analyzed for fetal gender, genetic abnormalities anddisease states by methods such as FISH, polymerase chain reaction (PCR),karyotyping, or similar methods or they can be used for research orpossibly therapeutic purposes.

As disclosed herein, the inventive methods provide for isolation offetal cells from a variety of biological fluids, including but notlimited to peripheral blood, plasma or serum thereof, and saliva.

The present invention provides minimally invasive methods for detectingand capturing cells of fetal origin from maternal peripheral blood. Dueto the rarity of fetal cells in an adult biological fluid such asmaternal blood, the methods of this invention include the step ofremoving more numerous maternal cells from a biological fluid, forexample maternal erythrocytes and platelets from a maternal bloodspecimen, using well-established techniques for sedimenting the specimenthrough a step-format density gradient using Ficoll or an equivalentmaterial as the denser medium. This process results in the erythrocytesbeing pelleted at the bottom of a centrifuge tube while the plateletsremain in the supernatant fluid. The mono-nucleated cells, including thefetal cells of interest, are concentrated at the boundary between themore and less dense media forming the gradient and can be recovered inrelatively pure form.

Using a maternal blood sample, the mono-nucleated cell fraction obtainedby density gradient sedimentation consists of a mixture of small numbersof cells of fetal origin and maternally derived hematopoietic stemcells, progenitor cells and precursor cells commingled with a largenumber of mature adult cells. The fetal cells and immature cells ofmaternal origin can be differentiated from the mature adult cells on thebasis of the cell surface antigens (markers) that are displayed by thecells. In particular, existing methods rely on antibodies thatspecifically bind to the CD34, CD133 and/or similar antigens expressedby immature cells to permit the immature cells of fetal and maternalorigin to be separated from the mature cells of maternal origin.Although the CD34, CD133 and similar antigens are not strictly unique toimmature blood cells, the other cell types that are known to expressthese antigens, including small vessel endothelial cells, embryonicfibroblasts, developing epithelial cells and certain types of nervecells, are unlikely to be present in significant numbers in a properlydrawn specimen of maternal blood.

Two general methods are routinely employed for the initial separation ofimmature blood cells of fetal and maternal origin (hereafter calledCD34⁺ cells) from mature blood cells. One of these methods, fluorescenceactivated cell sorting (FACS), relies upon selective detection of theimmature cells of interest by “labeling” these cells using antibodiesthat have been conjugated to a fluorescent reporter moiety and thatspecifically bind to antigens such as CD34 that are expressed by theimmature cells. In this method, the mono-nucleated cell fractionobtained by density gradient sedimentation is treated with one or moreappropriate fluorescently conjugated antibodies and processed by FACS,which individually examines and classifies each cell based uponfluorescence intensity, forward scatter and side scatter. FACS divertsindividual cells that meet pre-determined fluorescent intensity, forwardscatter and side scatter criteria (specific for immature cells) into acollection vessel. The cells collected in this vessel are presumptivelythe desired immature cells of fetal and maternal origin.

Alternative methods can be used for this initial separation of immatureblood cells of fetal and maternal origin from mature blood cells. Theseinclude methods using antigen-specific antibodies to specificallyimmobilize cells of interest onto an insoluble support that can readilybe separated from the mixture being resolved. Numerous variations ofthis approach can be practiced in the collection of fetal cells frommaternal blood. For example, antibodies specific for CD34, CD133 orsimilar markers of immature cells are immobilized on the surfaces ofmagnetic microparticles. When combined with the mono-nucleated cellfraction obtained by density gradient sedimentation, these antibodiesbind to their corresponding antigens thereby capturing the cells thatdisplay these antigens on the surfaces of the magnetic microparticles.Application of a strong magnetic field causes these magneticmicroparticles with captured cells to be held against the sides of thecolumn or container in which this process is being performed, thusallowing the cells that do not display these antigens and, therefore,are not bound to magnetic microparticles, to be eluted. Themicroparticle-bound cells can then be released from the microparticlesand collected as a fraction that is substantially enriched in the cellsof interest. Another example of these methods selectively depletes thesample of mature cells in an initial separation and subsequentlycaptures the immature cells as described. This initial depletion ofmature cells, which is sometimes referred to as “negative selection”, isgenerally regarded as improving the capture efficacy in the second step.The capture antibodies employed for depleting mature cells are specificfor antigens that are specifically expressed by mature cells and areoften used as “cocktails” containing multiple antibodies, each of whichis specific for a different mature cell marker.

The cell fractions obtained using antibodies specific for CD34 and/orother antigens expressed by immature cells consist of mixturescontaining predominantly immature cells of both fetal and maternalorigin. Such mixtures are the end products of many of the methods thathave been published and/or patented for the recovery of fetal cells frommaternal blood. These mixtures have limited utility for diagnosticapplications, such as in those cases where the fetus is male and thefetal cells in the mixture can be identified by detection of thepresence of a Y-chromosome, and in some therapeutic applications wherethe substantial engraftment and proliferative capabilities of CD34⁺cells are beneficial. Other applications, however, require that thesample be further enriched in cells of fetal origin relative to those ofmaternal origin.

It has been demonstrated that the proliferative capacity of CD34⁺ cellsof fetal origin are substantially greater than those of CD34⁺ cells ofmaternal origin. This difference in proliferative capacity can beemployed to differentially enrich the fetal component of these samplesby expanding the cells of the sample in the presence of cytokines andother factors that promote the proliferation of CD34⁺ cells. Under suchconditions, the percentage of CD34⁺ cells of fetal origin in the sampleis increased in each cell division cycle thus enriching the sample inCD34⁺ cells of fetal origin.

These fetal cell-enriched cell populations are inadequate for manydiagnostic procedures, which are best performed using samples consistingalmost entirely of cells of fetal origin. Attempts to achieve this endhave largely focused upon identifying antigens that differentiatebetween fetal and maternal CD34+ cells, preparing antibodies thatspecifically bind to these antigens; and using these antibodies inseparation procedures as described above. These antigens have beenidentified and/or antibodies against unidentified fetal cell-specificantigens prepared using empirical methods. For example, antibodiesspecific for known cellular antigens are screened against panels ofnominally pure fetal and maternal cells, often prepared in accordancewith the methods described above, to identify those antibodies thatapparently preferentially bind to fetal cells. Alternatively, a hostanimal such as a mouse can be immunized with nominally purified fetalcells as an immunogen, and hybridomas prepared from the resulting immunecells. These hybridomas are the sub-cloned to homogeneity, for example,by limiting dilution and screening the antibodies produced by thesehybridomas against panels of nominally purified fetal and maternal cellsprepared as previously described. These methods can in theory produceantibodies useful for specific detection and/or capture of fetal cellsfrom maternal blood. However, the functional quality of these antibodiesis critically dependent upon the purity and homogeneity of the immunogenused to produce them, the comprehensiveness of the fetal and maternalcell panels employed for antibody screening, and the purity andhomogeneity of the members of these panels, defects in any of which canlimit the usefulness of these antibodies. This is a particular problemwith regard to the fetal and maternal cells used to produce theseantibodies, which are enriched for fetal cells but are not purepreparations thereof. Furthermore, even if the cells used are purely offetal or maternal origin, these preparations consist of mixtures ofcells at different stages of differentiation that display differingconstellations of antigens. Thus antibodies prepared according to thesemethods will, at best, recognize only a subset of the fetal cells thatare present in a sample.

These limitations in the art for preparing fetal cell-specificantibodies is addressed by the present invention. Rather than usingantibodies to cross-specific cell surface markers, antigen discovery wasperformed using pooled CD34⁺ cells prepared as described above. Twoseparate cell pools were prepared, one from maternal peripheral bloodfrom a non-pregnant donor and the other from fetal liver. The first poolthus consisted of CD34⁺ cells solely of maternal origin while the secondconsisted of CD34⁺ cells solely of fetal origin. Each pool of cells wasthen separately expanded in the presence of cytokines and other factorsthat promoted proliferation but not differentiation of CD34⁺ cells.After optional repurification of these expanded pools, they wereexpanded a second time in the presence of cytokines and other factorsthat promoted the differentiation of CD34+ cells to a stage thatexpresses CD36 antigen but not CD34 antigen and promoted proliferationof CD36⁺ cells. In addition to increasing the numbers of cellsavailable, this forced shift in cell phenotype reduced the percentage ofthe pools that consisted of cells that could not differentiate to aCD36-expressing state and collapsed the multiple CD34+ phenotypes thatcan so differentiate into a smaller number of phenotypes that expressedconsistent levels of CD36. Positive or negative selection can be used tofurther purify these CD36⁺ pools if desired. This process yieldeddefined pure preparations of cells of maternal and fetal origin.

The proteins expressed by these viable, purified adult and fetal cellpreparations were determined by extracting the total RNA from the cellsof each preparation; synthesizing the corresponding labeled cDNAmixtures from this RNA; hybridizing these cDNA mixtures to separate, butidentical “gene array” chips; and determining the amount of cDNA bindingto each of the probes in the gene arrays in accordance with standardprocedures known to those skilled in the art. These data were thenevaluated to identify those genes that were strongly expressed by CD36⁺fetal cells, but not significantly expressed by CD36⁺ maternal cells. Adecision threshold (Wilcoxon Signed Rank Test p-value of >0.99, morepreferably >0.999, even more preferably >0.9999) was typically employedin making these determinations (as disclosed in “Genechip ExpressionAnalysis Technical Manual, PN701024 Rev 3, 2004, Affymetrix Santa ClaraCalif.).

The amino acid sequence of the protein product of each gene determinedto be uniquely expressed by CD36⁺ cells of fetal origin, and the aminoacid sequences of all proteins significantly expressed by maternal CD36⁺cells were determined, typically by reference to standard databases ofsuch information such as Gene Bank and SwissProt. The amino acidsequences of these proteins were then searched to identify amino acidsub-sequences, typically of between 10 and 30 amino acid residues inlength, that appeared in proteins of fetal origin but not in proteins ofmaternal origin. The peptides identified in this manner were taken to beunique markers for CD36⁺ fetal cells. These unique peptides werechemically synthesized and antibodies raised against these peptides inaccordance with conventional techniques. In some cases it was desirableto modify the peptide through the addition of a N-terminal cysteineresidue or a C-terminal cysteinyl-alanine dipeptide in order tofacilitate preparation of the corresponding immunogen. The resultingantibodies were screened against purified CD36⁺ cells of fetal andmaternal origins to verify their specificity for binding to fetal cells.These antibodies were conjugated to fluorophores for use in FACSanalysis and/or separation, or conjugated to magnetic microparticles foruse in the magnetic recovery of fetal cells as needed. This procedureidentified both extracellular and intracellular protein antigens thatare unique to CD36⁺ fetal cells. Antibodies against the extracellularantigens can be used to capture CD36⁺ fetal cells; in FACS methods whereit is desirable to detect and/or collect viable CD36⁺ fetal cells; andin microscopic methods where it is desirable to detect and/or collectCD36⁺ fetal cells independent of viability. Intracellular antigens, onthe other hand, are useful for detecting and/or collecting CD36⁺ fetalcells using FACS methods where cell viability is not a concern and inmicroscopic methods where it is desirable to detect CD36⁺ fetal cells.

As provided herein, the antibodies of the invention specifically bind toepitopes comprising peptide fragments of cell surface proteins expressedby fetal cells. Preferably, the epitopes comprising these peptides areavailable for immunological binding by the antibodies of the inventionon the cell surface, most preferably the exterior cell surface, of fetalcells. Preferably, the antibodies are capable of immunologicallyspecific binding to cell surface antigens on fetal cells preferentiallyto binding on maternal cells, due inter alfa to greater expression ofthe antigen on the fetal cell surface; better conformational arrangementof the antigenic protein on the fetal cell surface; or presence on thefetal cell surface and absence on the maternal cell surface.

As used herein, the term “preferentially bind” or “preferential binding”will be understood to mean that the antibodies and fragments thereofprovided by the invention, as well as mixtures of such antibodies orantibody fragments, bind to fetal cells with an affinity or avidity thatis about 5 to about 200-fold, more preferably 10- to 100-fold, and evenmore preferably 20- to 50-fold higher than said antibodies and fragmentsthereof bind to maternal cells.

It will be further understood by those with skill in the art that theantibodies and fragments thereof provided by the invention includeantisera, purified polyclonal antibodies and fragments thereof, as wellas mixtures thereof, provided alone or in combination, and further cancomprise antibodies or antisera raised by conventional methods usingpurified fetal cells, and more preferably antigenic peptides obtainedfrom said cells, and even more preferably peptide antigens produced byin vitro chemical or other synthetic routes and used as an immungenaccording to conventional methods. In particular, the invention alsocomprises monoclonal antibodies and fragments thereof, and moreparticularly combinations of a plurality of said monoclonal antibodies.Said antibodies can be produced according to the methods set forthherein, or antibodies raised by any method to be immunologicallyreactive with an antigen expressed preferentially on a fetal cell.

These antibodies can be advantageously employed for recoveringhematopoietic cells of fetal origin from maternal peripheral blood.These embodiments of the inventive methods are practiced by obtaining asample of peripheral blood from a pregnant mother; isolating themononuclear cell fraction from this blood sample; collecting the CD34⁺sub-fraction of these mononuclear cells; optionally expanding theseCD34⁺ cells; expanding these cells in the presence of cytokines thatpromote the differentiation of these cells to a CD34-/CD36+ phenotype;and capturing or labeling the CD36+ cells of fetal origin that arepresent in this sample through the use of one or more of the antibodiesof this invention.

The invention thus provides antibodies, preferably monoclonalantibodies, that are specific for CD36+ cells of human fetal origin. Thepresent invention also encompasses antibody fragments, including but notlimited to F(ab) and F(ab)′₂ fragments, of such antibodies. Antibodyfragments are produced by any number of methods, including but notlimited to proteolytic or chemical cleavage, chemical synthesis orpreparation of such fragments by means of genetic engineeringtechnology. The present invention also encompasses single-chainantibodies that are immunologically reactive with an epitope specificfor a cell of fetal cell origin, made by methods known to those of skillin the art.

The following detailed examples are included to demonstrate preferredembodiments of the invention. It should be appreciated by those of skillin the art that the techniques disclosed in therein represent techniquesthat function well in the practice of the invention, and thus can beconsidered to constitute preferred modes for its practice. However,those of skill in the art should, in light of the present disclosure,appreciate that many changes can be made in various embodimentsdisclosed and still obtain a like or similar result without departingfrom the spirit and scope of the invention.

Example 1 Preparation of Fetal Liver Cells

Fetal liver cells were obtained from Cambrex Bio Science, Walkersville,Md.). Alternatively, such cells can be isolated from fetal livers (FL,gestational ages 15-22 weeks) from 5 different donors as follows.

Fetal livers from five donors are homogenized and passed through a wiremesh in the presence of a DPBS/0.2% BSA solution, where DPBS has aformula of Ca⁺⁺/Mg⁺⁺-free Dulbecco's phosphate-buffered saline(Biowhittaker, Walkersville, Md.); BSA is bovine serum albumin (SigmaSt. Louis, Mo.), containing 50 μg/ml gentamicin sulfate (LifeTechnologies, Grand Island N.Y.). CD34⁺ cells can be isolated from thishomogenate according to either the MACS or FACS method described inExample 3. Alternatively, this homogenate may be further purifiedaccording to the following protocol prior to CD34⁺ cell isolationaccording to either the MACS or FACS method described in Example 3

Mature erythroid cells and other Lineage positive cells are removed fromthe homogenate by immunomagnetic bead depletion. Briefly, the homogenateis incubated with saturating amounts of glycophorin A (GPA) mAb(American Type Culture Collection, Rockville, Md.); the cells washedtwice by suspension/sedimentation in DPBS/BSA, incubated for 15 minuteswith BioMag goat-mouse IgG magnetic particles (Perseptive Biosystems,Framingham, Mass.); and the magnetic particle-bound GPA⁺ FL cells arecaptured by magnetic gradient separation in either a column or batchformat. The GPA⁻ FL cells, which are not bound by the magneticmicroparticles, are separated from the captured cells by elution withDPBS/BSA (column) or by decantation (batch) and subjected to stepdensity gradient separation by centrifugation for 25 minutes at 800 g(room temperature) using 1.077 g/ml Nycoprep (Life Technologies, GrandIsland, N.Y.) as the dense phase. The resulting light density fetalliver (LDFL) cells are collected from the gradient interface; washedwith DPBS/BSA and resuspended in 2 ml of 10 μg mouse IgG1 and IgG2a(Sigma) in DPBS/BSA to block non-specific binding of monoclonalantibodies used for further cell capture. The resulting GPA-LDFL cellsuspension is incubated for 30 minutes at 4° C. with the followingFITC-conjugated antibodies: anti-CD3, anti-CD4, anti-CD8, anti-CD11b,anti-CD14, anti-CD16 anti-CD19, anti-CD20, anti-CD36, anti-CD54(comprising the Lineage panel). After washing, the labeled cells aresubjected to negative selection using magnetic beads coated withsheep-anti-mouse IgG (Dynal, Oslo Norway) in the manner described aboveto yield GPA⁻Lin⁻ LDFL cells. CD34⁺ cells are then isolated from theresulting GPA⁻Lin⁻ LDFL cells using the either the MACS or FACS protocoldescribed in Example 3 below.

Example 2 Preparation of Mobilized Peripheral Blood Cells

Mobilized peripheral blood cells were obtained from Cambrex. Such cellscan also be obtained as follows.

G-CSF (granulocyte colony stimulating factor) mobilized peripheral blood(MPB) mononuclear cells are obtained by leukapherisis from ten differentnormal adult donors and isolated according to standard protocols knownto those of ordinary skill in the art. CD34⁺ cells can be isolated fromthis MPB blood fraction according to either the MACS or FACS methoddescribed in Example 3. Alternatively, this MPB blood fraction can befurther purified according to the following protocol prior to CD34⁺ cellisolation according to either the MACS or FACS method described inExample 3.

The mononuclear cell fraction is depleted of mature erythroid cells andother Lineage positive cells by immunomagnetic bead depletion asdescribed in Example 1. Briefly, mature erythroid cells and otherLineage positive cells are removed from the MPB blood fraction byincubating the cells with saturating amounts of glycophorin A (GPA) mAb;washing twice by suspension/sedimentation in DPBS/BSA; incubation for 15minutes with BioMag goat-mouse IgG magnetic particles (PerseptiveBiosystems); and separating the magnetic particle bound GPA⁺ MPB cellsfrom the unbound GPA⁻ MPB by magnetic gradient separation in either acolumn or batch format. The GPA″ MPB cells are subjected to step densitygradient separation by centrifugation for 25 minutes at 800 g (roomtemperature) using 1.077 g/ml Nycoprep (Life Technologies, Grand Island,N.Y.) as the dense phase. The resulting light density MPB cells arecollected from the gradient interface; washed with DPBS/BSA andresuspended in 2 ml DPBS/SBA supplemented with 10 μg mouse IgG1 andIgG2a (Sigma) to block non-specific binding of monoclonal antibodiesused for further cell capture. The resulting GPA-MPB cell suspension isincubated for 30 minutes at 4° C. with the following FITC conjugatedantibodies: anti-CD3, anti-CD4, anti-CD8, anti-CD11b, anti-CD14,anti-CD16 anti-CD19, anti-CD20, anti-CD36, anti-CD54 (comprising theLineage panel). After washing, the labeled cells are subjected tonegative selection using magnetic beads coated with sheep-anti-mouse IgG(Dynal, Oslo Norway) in the manner described in Example 1 above to yieldGPA⁻Lin⁻ MPB cells. CD34⁺ cells are then isolated from the resultingGPA⁻Lin⁻ MPB cells using the either the MACS or FACS protocol describedin Example 3 below.

Example 3 Purification of Adult and Fetal CD34⁺ Progenitor Cells

The fetal liver cells and MPB mononuclear cell fractions of Examples 1and 2, respectively, were enriched in CD34⁺ cells in accordance witheither of the following protocols:

MACS Protocol

The fetal liver cells and MPB mononuclear cell fractions prepared asdescribed in Examples 1 and 2, respectively, were immunomagneticallyenriched in CD34⁺ cells using a MACS CD34 Isolation Kit (MiltenyiBiotec, Auburn, Calif.) in accordance with the manufacturer'sinstructions. Briefly, the mononuclear cells were incubated withhapten-labeled anti-CD34 antibody (QBEND-10, BD Pharmingen, San Diego,Calif.) in the presence of 0.1% human IgG (Bayer Elkhart, IN) as ablocking reagent and then incubated with anti-hapten coupled to MACSmicrobeads. The labeled cells were filtered through a 30 μm nylon meshto remove cell clumps and aggregates. The labeled CD34⁺ cells were thencaptured from the mixture using a high-gradient magnetic separationcolumn (Miltenyi Biotec). After elution of the non-labeled CD34⁻ cells,the magnetic field was removed and the magnetically retained CD34⁺ cellswere eluted from the column with staining buffer SB (DPBS supplementedwith 0.2% BSA and 2 mM EDTA, pH 7.2) at 4-8° C. Greater than 90% of therecovered cells were CD34⁺ as determined by FACS (FACSCalibur; BectonDickinson San Jose Calif.) analysis using the CellQuest AnalysisSoftware (Becton Dickinson).

FACS Protocol

The fetal liver and mononuclear cell fractions prepared as described inExamples 1 and 2, respectively, were alternatively enriched in CD34⁺cells by Fluorescence Activated Cell Sorting (FACS). The fetal liver andmononuclear cell fractions were stained with 20 μl offluorescein-labeled anti-CD34 monoclonal antibody (catalog #34374X; BDPharmingen) per 1×10⁶ cells in SB for one hour at 4-8° C. Non-specificbinding control cells were stained in an identical manner withfluorescein-labeled isotype-matched murine IgG₁ (catalog #554679; BDPharmingen). Immediately prior to sorting, 1 μg/mL of the fluorescentDNA stain propidium iodide (PI) was added to each sample to permitidentification and exclusion of nonviable cells. Cells were sorted andanalyzed on a FACSVantage cell sorter (Becton Dickinson) in accordancewith the manufacturer's instructions. A 488 nm argon ion laser was usedfor excitation of the fluorophores, and fluorescence was detected at 525nm (fluorescein) and 620 nm (PI). Viable CD34⁺ cells (CD34⁺/PI⁻) werecollected and stored on ice until used. Sample cells exhibiting CD34fluorescence intensities greater than the 99^(th) percentile of thoseexhibited by the isotype-matched irrelevant murine IgG1 controls wereselected as being CD34⁺. Forward and side light scatter excluded cellaggregates or debris. Greater than 90% of the recovered cells were CD34⁺as determined by FACSCalibur (Becton Dickinson) analysis using theCellQuest Analysis Software (Becton Dickinson).

Example 4 Stimulation of Fetal CD34⁺ Cells to Express CD36

Fetal and adult CD34⁺ cells were isolated and purified as described inExample 3 and expanded by one of two methods. In one set of experiments,CD34⁺ cells were expanded using Hematopoietic Progenitor Growth Media(HPGM; Biowhittaker) supplemented with 50 ng/ml Flt-3 ligand (FLT-3),100 ng/ml TPO (thrombopoietin), and 100 ng/ml SCF (stem cell factor) forfrom four to six days at 37° C. under 5% CO₂ in liquid culture. Thesecells were then stimulated to express CD36 by further expansion in HPGMsupplemented with 3 U/ml EPO (erythropoietin), 25 ng/ml SCF, 10 ng/mlInterleukin-3 (IL-3), and 10 ng/ml Interleukin-6 (IL-6) for from four tosix days at 37° C. under 5% CO₂. Alternatively, CD34⁺ cells wereexpanded using HPGM supplemented (known hereinafter as “supplementedHPGM”) with 2% deionized bovine serum albumin, 150 μg/ml iron saturatedhuman transferring, 900 μg/ml ferrous sulfate, 90 μg/ml ferric nitrate,100 μg/ml insulin, 30 μg/ml soybean lecithin, and 7.5 μg/ml cholesteroland 1×10⁻⁶ M hydrocortisone (Sigma) wherein cells are cultured insupplemented HPGM containing 50 ng/ml Flt-3 ligand (FLT-3), 100 ng/mlTPO (thrombopoietin), and 100 ng/ml SCF (stem cell factor) for four tosix days at 37° C. under 5% CO₂ in liquid culture. These cells were thenstimulated to express CD36 by further expansion in supplemented HPGMcontaining with 3 U/ml EPO (erythropoietin), 50 ng/ml IGF-1(Insulin-like growth factor-1), and 50 ng/ml SCF for from four to sixdays at 37° C. under 5% CO₂. The CD36-expressing cells were recoveredand purified by MACS to greater than 85% purity as determined byFACSCalibur (Becton Dickinson) analysis using the CellQuest AnalysisSoftware (Becton Dickinson).

Example 5 Isolation of Total RNA

Total RNA was separately isolated from the CD36⁺ adult MPB and fetalliver cells using Trizol (Life Technologies, Gaithersburg, Md.)according to the manufacturer's instructions. Cells were pelleted andthen lysed by resuspension in 1 mL Trizol per 5×10⁶ cells by repeatedpipetting. The cell lysate was then incubated for 5 minutes at roomtemperature and extracted with 0.2 volumes chloroform by vortexing for 1minute. The sample was then centrifuged for 30 minutes at 13,000 rpm(12,000 g) at 4° C. in a microcentrifuge. The RNA was precipitated bythe addition of 2 volumes isopropanol, mixed and allowed to sit at roomtemperature for 10 minutes. The RNA was centrifuged for 45 minutes at 12000×g. The RNA pellet was washed with 75% ethanol, briefly dried;resuspended in RNase-free water or diethyl pyrocarbonate-treated (DEPC;Sigma) water (0.1%) and treated with RNase-free DNase I enzyme (LifeTechnologies) according to the manufacturer's instructions. The RNAconcentration was then determined by using a Beckman DU 650spectrophotometer (Beckman Instruments, Palo Alto, Calif.).Alternatively, the total RNA was isolated using the RNeasy RNA IsolationKit (Qiagen, Valencia, Calif.) according to manufacturer's instructions.

Example 6 Preparation of cDNA for Microarray Analysis

cDNA for analysis on an Affymetrix GeneChip™ microarray was preparedaccording to the manufacturer's instructions as set forth in theGeneChip Expression Analysis Technical Manual (Affymetrix, Santa Clara,Calif.). Briefly, total RNA was isolated from adult MPB and fetal livercells as described in Example 4 and reverse transcribed using aT7-Oligo(dT) Promoter Primer in the first-strand cDNA synthesisreaction. The second-strand cDNA was synthesized in an Rnase-H-mediatedreaction and the resulting double-stranded cDNA purified. The purifieddouble-stranded cDNA was transcribed in the presence of T7 RNAPolymerase and a mixture of biotinylated nucleotide analogs andribonucleotides to prepare complementary RNA (cRNA). The cRNA wasfragmented and hybridized to Affymetrix U133 arrays as described inExample 7.

Example 7 cDNA Microarray Analysis

The resulting fetal and adult cDNA preparations were separately analyzedusing Affymetrix U133 microarray chips according to the manufacturer'sinstructions. The corrected fluorescent intensities for thecorresponding genes on the fetal and adult microarray chips weremeasured and converted to p-values in accordance with standard methods(see, Statistical Algorithims Reference Guide, Affymetrix Inc. SantaClara, Calif.). Genes and Expressed Sequence Tags (EST) that were morestrongly expressed in the fetal cDNA samples (where the Wilcoxon'sSigned Ranked Test p-value (please see Genechip Expression AnalysisTechnical Manual for complete explanation) was greater or equal to 0.99,preferably >0.999 and more preferably 0.9999 were taken as beinguniquely expressed by CD36⁺ fetal cells relative to CD36⁺ adult cells.The genes that are preferentially expressed in fetal CD36+ cellsprepared in accordance with the present invention are listed in Table 1.The ESTs that are preferentially expressed in fetal CD36+ cells preparedin accordance with the present invention are listed in Table 2.

TABLE 1 Genes that are Preferentially Expressed by CD36⁺ Fetal LiverCells Wilcoxon Gene name FL/MPB Ranked (Genbank/Unigene Accession No.)signal ratio p value AD037 (AI890191) 1976/9.1  0.99998 CSPG2(NM_004385) 1959.5/29.4  0.99998 DCNP1 (Hs.152477) 968.6/86.7 0.99998Homo sapiens cDNA FLJ30298 fis, 700.5/2.8  0.99998 clone BRACE2003172(AK025198.1) Homo sapiens cDNA FLJ33028 fis, 2228.3/7.4  0.99998 cloneTHYMU2000140 (AL048542) Homo sapiens cDNA: FLJ21545 fis, 4129.6/21  0.99998 clone COL06195 (AK025198.1) KCNJ2 (AF153820) 244.6/18.2 0.99998MRC1 (NM_002438) 2036.7/23.1  0.99998 MS4A4A (NM_024021) 126.9/7.9 0.99998 MS4A6A (NM_022349) 5229.9/44.5  0.99998 MS4A7 (Hs.530735)2661.9/60.7  0.99998 NMES1 (AF228422.1) 116.9/10.1 0.99998 PAG(NM_018440.1)  981/96.2 0.99998 PARVG (AF237772.1)  701/17.2 0.99998S100A8 (AW238654) 7132.9/31.3  0.99998 S100A9 (NM_002965) 2518/15 0.99998 ASGR2 (NM_001181) 1274.2/4.8  0.99998 C1QG (AI184968)1399.7/6.1  0.99998 TIM3 (AW025572) 415.17/18.8  0.99998 HRB2(Hs.205558) 1064.6/59.9  0.99997 PKIB (Hs.486354) 339.8/5.4  0.99997MAFB (Hs.169487) 797.4/81.3 0.99996 MGC21854 (AI659418)  911.1/148.90.99996 PRAM-1 (Hs.465812) 276.6/15.8 0.99996 AKNA (Hs.494895)661.1/37.7 0.99992 AD026 (AF226731.1) 198.3/10.3 0.99990 GPR84(AF237762.1)  411/21.3 0.99985 JDP2 (Hs.196482)  875/12.5 0.99985 RCP(BE544375) 145.9/13.4 0.99969 RASGRP4 (Hs.130434) 493.9/20.9 0.99956PTGFRN (Hs.418093) 137.8/20  0.99817 CXCL16 (Hs.82407) 327.4/76.60.99775 CREM (Hs.200250) 241.4/21.4 0.99751 MS4A5 (Hs.178066) Data NotAvailable MS4A10 (Hs.450640) Data Not Available

TABLE 2 ESTs that are Preferentially Expressed by CD36⁺ Fetal LiverCells EST WITH GENBANK FL/MPB ACCESSION NUMBER signal ratio p valueAL039884  740.5/35.5 0.99998 AV646597 1612.5/63.5 0.99998 AW135176 1820/77.8 0.99998 AW872374  699.2/37.9 0.99998 BF892532 322.6/8.60.99998 AI536637 288.8/9.9 0.99998 BE549540  766.7/34.4 0.99998 AW303397 695.4/14.4 0.99997 AI741439 221.6/7.9 0.99994 AV660825 102.2/3.80.99992 AI681260 183.9/3.6 0.99990 AW006441   611/13.4 0.99990 AW575863 374.4/10.4 0.99990 AI915629  113/4.4 0.99951 AA988769   94/2.6 0.99914AV688087 279.5/9.4 0.99914

TABLE 3 Amino Acid Sequences of Unique PeptidesCorresponding to Selected Genes Gene Peptide A Peptide B MS4A10NTTQPKLLAPHQHEKSQKKS CINALSSNLKSPRLSQPAEE (SEQ ID NO. 1) (SEQ ID NO. 2)MS4A7 FTPKGITIPQREKPGHMYQN YSNNPGSSFSSTQSQDHIQQ (SEQ ID NO. 3)(SEQ ID NO. 4) MS4A6A FSQAEKPEPTNQGQDSLKKH PASLQCELDKNNIPTRSYVS(SEQ ID NO. 5) (SEQ ID NO. 6) ASGR2 HELGGSEDCVEVQPDGRWNDLQVYRWVCEKRRNATGEVA (SEQ ID NO. 7) (SEQ ID NO. 8) MS4A5MDSSTAHSPVFLVFPPEITA TFGFILDQNYICGYSHQNSQ (SEQ ID NO. 9) (SEQ ID NO. 10)

Example 8 Antibody Production

The amino acid sequences of the proteins corresponding to the genes andEST's identified in Example 7 were determined by reference to GenBank,SwissProt and other publicly available sources. Each of these amino acidsequences was evaluated to identify peptide regions within each proteinthat had unique amino acid sequences. Where possible, two or more suchpeptide regions were identified for each protein. By way of example, theamino acid sequences of two unique peptide regions of the proteinsencoded by the genes MS4A10, MS4A7, MS4A6A, ASGR2, MS4A5 are listed inTable 3.

A N-terminal cysteine residue was added to the MS4A10 (SEQ ID No.11/12), MS4A7 (SEQ ID NO. 13/14) and MS4A6A (SEQ ID NO. 15/16) peptidesand the dipeptide CYS-ALA was added to the C-terminal of the MS4A5 (SEQID NO. 17/18) peptides to facilitate conjugation of these peptides toKeyhole Limpet Hemocyanin during the preparation of the immunogen.

These peptides were synthesized using conventional methods andpolyclonal antisera and purified rabbit polyclonal antibodies wereobtained from Bethel Labs, Montgomery, Tex.; said antisera and purifiedantibodies can be produced from said polyclonal antisera using methodsthat are well known to those skilled in the art (see, for example,Harlow & Lane, 1988, Antibodies: A Laboratory Manual, Cold Spring HarborLaboratory Press: New York). The resulting antibodies were affinitypurified and conjugated to the hapten biotin or the fluorophorefluorescein or phycoerythrin (PE) depending upon the intended use of theantibody conjugate thus produced.

Example 9 Isolation of CD34⁺ Cells from Maternal Peripheral Blood

Peripheral blood (PB) samples were obtained in heparinzined collectiontubes by venipuncture of pregnant female donors who were known by anindependent means such as amniocentesis to be carrying a male fetus. TheY-chromosome of the fetus provided a definitive means of differentiatingbetween otherwise identical cells of maternal and fetal origins. Thecollected peripheral blood was diluted with DPBS, underlaid withFicoll-Paque (Pharmacia AB) and centrifuged at 800 g for 30 minutes at20° C. The mononuclear cell fraction was collected from the buffy coatand were stained with 20 μl/10⁶ cells of fluorescein-labeled anti-CD34monoclonal antibody (catalog #34374X; BD Pharmingen) in SB for one hourat 4-8° C. Immediately prior to sorting, 1 μg/mL of the fluorescent DNAstain PI was added to each sample to permit identification and exclusionof nonviable cells. Cells were sorted and analyzed on a FACSVantage cellsorter (Becton Dickinson) in accordance with the manufacturer'sinstructions. A 488 nm argon ion laser was used for excitation of thefluorophores while detection was at 525 nm (fluorescein) and 620 nm(PI). Alternatively, cells were processed following the MACS protocol asdescribed in Example 3. The CD34⁺ sub-population (viable CD34⁺ cells)was collected and stored on ice until used. By these methods, between500 to 3000 viable CD34+ cells could typically be obtained from anapproximately 30 ml sample of whole blood from a female donor, which isabout 70-85% of the number of CD34+ cells expected from such a sample.

Example 10 Stimulation of CD36 Expression by CD34⁺ Cells from MaternalPeripheral Blood

The CD34⁺ cells isolated as described in Example 9 were expanded eitherin Hematopoietic Progenitor Growth Media (HPGM; Biowhittaker)supplemented with either 3 U/ml EPO (erythropoietin), 25 ng/ml SCF, 10ng/ml Interleukin-3 (IL-3), and 10 ng/ml Interleukin-6 (IL-6) for threeto six days at 37° C. under 5% CO₂ or in supplemented HPGM containing 2%deionized bovine serum albumin, 150 μg/ml iron saturated humantransferring, 900 μg/ml ferrous sulfate, 90 μg/ml ferric nitrate, 100μg/ml insulin, 30 μg/ml soybean lecithin, and 7.5 μg/ml cholesterol and1×10⁻⁶ M hydrocortisone (Sigma) and further containing 50 ng/ml Flt-3ligand (FLT-3), 100 ng/ml TPO (thrombopoietin), and 100 ng/ml SCF (stemcell factor) for four to six days at 37° C. under 5% CO₂ in liquidculture. These cells were then stimulated to express CD36 by furtherexpansion in supplemented HPGM containing with 3 U/ml EPO(erythropoietin), and 50 ng/ml IGF-1 (Insulin like growth factor-1) forfrom four to six days at 37° C. under 5% CO₂ to drive the cells toexpress CD36

Example 11 Separation of Fetal Cells from Maternal Blood by FACS

The phenotype-shifted CD36⁺ cells prepared as described in Example 10were immuno-stained with phycoerythrin (PE) conjugated anti-CD36 (BDPharmingen) and purified polyclonal antibodies (Bethel Labs, Montgomery,Tex.) selected from among those prepared in accordance with Example 7,conjugated to either fluorescein or biotin. If a biotin conjugatedantibody was used, a streptavidin-APC (allophycocyanin) (BD Pharmingen)conjugate was used as the detection reagent. All immuno-staining wasperformed according to standard methods at 4-8° C. in aphosphate-buffered saline (DPBS) buffer (pH 7.4) containing 0.2% BSA.Prior to antibody staining, cells were incubated with 1% Gamimune (BayerHealth Care Research Triangle Park, N.C.) for 30 minutes at 4-8° C. toblock non-specific antibody binding. The immuno-stained cells weresorted and analyzed on a FACSVantage cell sorter (Becton Dickinson) inaccordance with the manufacturer's instructions. A 488 nm argon ionlaser was used for excitation of the fluorophores while detection was at525 nm (fluorescein) and 575 nm (PE and APC). Those cells that stainedpositively for both CD36 and the target peptide were collected andstored on ice until used. Control cells were incubated withfluorochrome-conjugated isotype-matched IgM-fluorescein (BD Pharmingen),IgM-PE (BD Pharmingen) or anti-rabbit isotype controls. Cell aggregatesor debris were excluded by gating on forward and side light scattering.

Example 12 Magnetic Separation of Fetal Cells from Maternal Blood

The phenotype-shifted CD36⁺ cells prepared as described in Example 10were immuno-stained with phycoerythrin (PE) conjugated anti-CD36 (BDPharmingen) and a biotin-conjugated antibody selected from among thoseprepared in accordance with Example 7. The doubly-labeled cells wereincubated with streptavidin-conjugated MACS microbeads (Miltenyi Biotec)and filtered through a 30 μm nylon mesh to remove cell clumps andaggregates. Cells expressing the selected fetal cell marker were thencaptured from the mixture using a high-gradient magnetic separationcolumn according to the manufacturer's instructions. After elution ofthe non-retained cells, the magnetic field was removed and themagnetically retained fetal cells were eluted from the column with SB.The CD36⁺ fetal cells in this eluate were those that were also labeledwith PE. All immuno-staining was performed according to standard methodsat 4-8° C. in a DPBS buffer (pH 7.4) containing 0.2% BSA.

Example 13 Detection of Gene Expression Using RNA Probes

Fetal cell expression of the genes identified in Example 7 isdemonstrated using RNA probes. Briefly, RNA templates corresponding toone or more of the genes identified as described in Example 7 areprepared according to the protocol provided using the Promega T-7Riboprobe In-vitro Transcription System (Promega, Madison, Wis.) inaccordance with its instructions or can be purchased inter alfa fromGeneDetect.com (Auckland, NZ). 5′-(α′³⁵S)rUTP can be obtained fromAmersham Pharmacia Biotech (Piscataway, N.J.) or NEN/Perkin Elmer(Boston, Mass.). All other reagents can be obtained from Promega unlessotherwise noted. Buffers are prepared in accordance with theinstructions provided for the GeneDetect One-Step RNA Probe SynthesisTemplates unless otherwise specified.

RNA Probe Preparation

RNA probes are prepared as follows. Two μl of 5× Transcription Buffer, 1μl of 100 mM dithiothreitol (DTT), 1 μl of Rnasin Rnase inhibitor; 1 μgof the desired RNA template(s) in 3 μl water; and a mixture containing 5μM each of GTP, CTP and ATP in 2 μl of Transcription Buffer is added to25 μl of ³⁵S-UTP lyophilized into the bottom of a 1.5 mL microfuge tube.After mixing, 1 μl of T7 RNA Polymerase is added to the mixture, mixedand incubated for one hour at 30° C. To ensure complete transcription, asecond 1 μl aliquot of T7 RNA Polymerase is added to the mixture, mixedand incubated for an additional one hour at 30° C. before stopping thereaction by the addition of 1 μl of RQ1 Dnase and incubating for 15minutes at 37° C. The RNA probe is recovered from the reaction mixtureby the addition of 24 μl of 10 mM Tris-HCl/1 mM EDTA (pH 8.0) buffer(TE) and 50 μg of tRNA; vortexing; and desalting on a G-50 Sephadexcolumn (Amersham Pharmacia Biotech). Probe integrity is confirmed byelectrophoresis on a 15% polyacrylamide gel in Tris-Borate-EDTA(TBE)-Urea buffer.

Fetal Cell Staining Using RNA Probes

CD36⁺/peptide⁺ cells collected by FACS as described in Example 11 or bymagnetic separation as described in Example 12 are prepared as monolayercellular preparations on a glass microscope slide by settling, CytoSpin(Thermo-Shandon, Pittsburgh, Pa.), ThinPrep (Cytyc, Boxborough, Mass.)or similar standard method. The cells are covered with 1000 ofhybridization buffer (HB) and incubated at 42° C. for 1-3 hours topermeabilize the cells. For each slide to be processed, 20 of thedesired RNA probe and 1 μl of 50 mg/mL tRNA are combined, heated to 95°C. for 3 minutes and cooled by the addition of 17 μl of HB. 20 μl of theresulting mixture added to the 100 μl droplet of HB on the slide andincubated overnight at 45-55° C. The labeled specimens are then washedtwice for 10 minutes each with 2×SSC-BME-EDTA at room temperature;immersed in a 20 mg/ml solution of Rnase A for 30 minutes at roomtemperature; washed twice for 10 minutes each with 2×SSC-BME-EDTA atroom temperature; washed for 2 hours with 4 L of 0.1×SSC-MBE-EDTA;washed 2×10 minutes in 0.5×SSC at room temperature; dehydrated for 2minutes each in 50%, 70% and 90% ethanol containing 0.3M ammoniumacetate and dried in a vacuum desiccator. Labeled cells are detected byautoradiography in the standard manner.

Example 14 Diagnostic Testing of Fetal Cells: Microscopic Detection andEvaluation of Fetal Cells Isolated from Maternal Blood

CD36⁺/peptide⁺ cells that can be collected by FACS as described inExample 11 or by magnetic separation as described in Example 12 areprepared as monolayer cellular preparations on a glass microscope slideby undisturbed settling, CytoSpin (Thermo-Shandon, Pittsburgh, Pa.),ThinPrep (Cytyc, Boxborough, Mass.) or similar method, immuno-stained aspreviously described; and evaluated using fluorescence microscopy inaccordance with methods known to those skilled in the art. The presenceof cells that stain positively for both CD36 and the target peptide isindicative of the presence of fetal cells in the preparation. Thepreparation may be subsequently counterstained in-situ with a chromaticstain such as hemotoxylin and the cells therein evaluatedmorphologically or subjected to an in-situ hybridization staining methodsuch as fluorescence in situ hybridization (FISH) to detect the presenceof specific genes or mutated genes within the cells in the preparation.Such counterstainings are performed according to procedures that areknown to those skilled in the art. If the physical locations of theCD36⁴/peptide⁺ cells within the preparation are determined, thislocation information can be used to correlate the results obtained bymorphological analysis or in-situ hybridization with specific fetalcells in the preparation. Such correlations between CD36⁴/peptide⁺ cellsand the same cells subsequently stained with additional reagents canreadily be performed using commercially available automated microscopysystems such as exemplified by the AcCell or TracCell computer assistedmicroscopy systems (Molecular Diagnostics, Chicago, Ill.).

Example 15 Diagnostic Testing of Fetal Cells: PCR Detection of theY-chromosome in Cells from a Male Fetus Isolated from Maternal Blood

The CD36⁺/peptide⁺ cells collected by FACS as described in Example 11were tested by PCR to determine whether they contained a Y-chromosome.Briefly, whole genomic DNA was extracted from isolated cells by modifiedsalt precipitation method (Puregene DNA Isolation Kit, Gentra systems,Minneapolis, Minn.). Approximately 50-200 ng of DNA was analyzed byconventional Polymerase Chain Reaction (PCR) for both the GAPDH and SRYloci, using a GeneAmp PCR system 9700 Thermocycler (Perkin Elmer, FosterCity, Calif.), Platinum Taq DNA Polymerase (Invitrogen Corporation,Carlsbad, Calif.) as an enzyme, and the following procedure. Thin-walledPCR micro-tubes were first incubated at 94° C. for 2 minutes to denaturethe sample and activate the enzyme. Samples were then subjected to 10cycles of amplification (the first 5 cycles consisting of a 15 secondsdenaturation step at 94° C., 30 second annealing step at 59° C., withthe subsequent 5 cycles consisting of a 15 second denaturation step at94° C., 30 second annealing step at 57° C.,) followed by 30 cyclesconsisting of a 15 second denaturation step at 94° C., 30 secondannealing step at 55° C.). This was followed by a final extension stepfor 10 minutes at 72° C. The SRY sequence was used to measure thepresence of fetal DNA, while the glyceraldehyde-3-phosphatedehydrogenase (GAPDH) sequence was used to confirm the integrity andquality of DNA in each sample. The following oligonucleotides were used:SRY forward 5′-TCC TCA AAA GAA ACC GTG CAT-3′ (SEQ ID NO. 19), SRYreverse 5′-AGA TTA ATG GTT GCT AAG GAC TGG AT-3′ (SEQ ID NO. 20), GAPDHforward 5′-CCC CAC ACA CAT GCA CTT ACC-3′ (SEQ ID NO. 21) and GAPDHreverse 5′-CCT AGT CCC AGG GCT TTG ATT-3′ (SEQ ID NO. 22). The PCRproducts were separated by 2% agarose gel electrophoresis, and thepresence of a Y-chromosome specific fragment obtain from DNA from thesecells demonstrated that they originated from the (male) fetus ratherthan from the mother. By substituting the appropriate primers for theY-chromosome primer, PCR analysis may employed in a similar manner todetect the presence of specific genes and mutated genes in the collectedcells including ones that have been correlated with the presence ofparticular disease states. Similarly, the collected cells may besubjected to analyses by methods such as FISH if suitable probes areemployed.

Example 16 Diagnostic Testing of Fetal Cells: RT-PCR Detection of theY-chromosome in Cells from a Male Fetus Isolated from Maternal Blood

Real time quantitative PCR analysis is performed on isolated fetal cellsas described in Example 11 using ABI PRISM 7700 Sequence DetectionSystem (Applied Biosystem, Foster City, Calif.), As an internal control,the β-globin TaqMan system can be used consisting of two primersβ-globin-354 (forward), 5′-GTG CAC CTG ACT CCT GAG GAG A-3′ (SEQ ID NO.23); (β-globin-455 (reverse), 5′-CCT TGA TAC CAA CCT GCC CAG-3′ (SEQ IDNO. 24) and a dual-labeled fluorescent TaqMan probe β-globin-402T,5′(FAM) AAG GTG AAC GTG GAT GAA GTT GGT GG (TAMRA)-3′ (SEQ ID NO. 25).To detect the presence of Y chromosome in isolated fetal samples aspreviously described, the SRY TaqMan system can be used consisting ofSRY-109 (forward) primer, 5′-TGG CGA TTA AGT CAA ATT CGC-3′ (SEQ ID NO.26); SRY-245 (reverse) primer, 5′-CCC CCT AGT ACC CTG ACA ATG TAT T-3′(SEQ ID NO. 27) and a probe SRY-142T, 5′(FAM) AGC AGT AGA GCA GTC AGGGAG GCA GA (TAMRA)-3′ (SEQ ID NO. 28). TaqMan amplification reactionsare set up in a reaction volume of 25 μl using the TaqMan Universal PCRMaster Mix (Applied Biosystems). DNA amplifications are carried out in8-well reaction optical tubes/strips (Applied Biosystems). The TaqManPCR conditions are used as described in TaqMan guidelines using 40cycles of 95° C. for 15 s and 60° C. for 1 min. with 2-min preincubationat 50° C. required for optimal AmpErase UNG activity and 10-minpreincubation at 95° C. required for activation of AmpliTaq Gold DNApolymerase. Each sample was analyzed in triplicate. A calibration curveis run in parallel with each analysis.

Example 17 Diagnostic Testing of Fetal Cells: FISH Determination of theSex of a Fetus using Fetal Cells Isolated from Maternal Blood SlidePreparation

Cells of fetal origin isolated as described in Examples 11 or 12,respectively, are pelleted in 15 mL screw-capped tubes using a table-topcentrifuge and washed once with HPGM containing 10 U/mL of heparin (ICNBiomedicals Inc, Aurora, Ohio). The cells are resuspended in 100 to 2004of HPGM/heparin. A PAP pen (Research Products International, Mt.Prospect, Ill.) is used to mark a rectangle on silane-treated slides,and 100 to 200 μL of cell suspension is spread throughout the rectangle.Slides are incubated for 30 to 45 minutes at room temperature (RT) toallow the cells to settle and attach to the slides. Excess liquid isremoved by tipping the slides sideways and the slides air-dried. Theslides are fixed with methanol:acetic acid (3:1) for 15 minutes andallowed to air-dry. Slides are stored at −80° C. until use.

Fluorescent In Situ Hybridization (FISH)

On the day of hybridization, the specimens are thawed at roomtemperature (RT), refixed with methanol:acetic acid (3:1), air-dried,and pretreated by incubation for 30 minutes at 37° C. in 2×SSC (3M NaCl,0.3M sodium citrate, pH 7.0). This is followed by dehydration in aseries containing ethanol at 70, 90, and 100% concentrations at RT. Thespecimens are then treated with pepsin (20 mg/ml, Sigma) to improveprobe penetration and denatured in 70% formamide/2×SSC for 2 minutes at72° C. followed by the dehydration series described above, on ice. 600μl of each alpha-satellite centromere specific probe for chromosomes Xand Y, 16.8 μl of CEP buffer (Vysis, Downers Grove, Ill.) and 2 μl ofwater are combined. The probe mixture is then denatured at 70° C. for 5minutes and applied to prewarmed (37° C.) target specimens. Thehybridization area is sealed with a glass coverslip and placed into an80° C. oven for 90 seconds. After an overnight hybridization at 37° C.in a humidified chamber, the coverslip and glue are removed. The slideis then washed in 0.25×SSC at 67° C. for 12 seconds and rinsed in 1×PBD(2-phenyl-5-(4-biphenyl)-1,3,4,-oxadiazole; ONCOR Gaithersburg, Md.) for1 minute. The specimens are then counterstained with DAPI(4,6-diamidino-2-phenylindole II; Vysis) for 10 minutes prior tomicroscopic analysis. The presence of X- and Y-chromosomes is determinedby fluorescence microscopy using a Zeiss Axioskop microscope (CarlZeiss, Thornwood, N.Y.).

The descriptions of particular antibodies and methods embodied above areintended to be representative of and not limiting to the presentinvention. Although the antibodies and methods of this invention havebeen described in terms of preferred embodiments, it will be apparent tothose skilled in the art that alternative implementations, compositionsand/or methods herein described can be made without departing from theconcept, spirit and scope of the invention. Specifically, it will beapparent that the antibodies herein described may be implemented byalternative means and that the compositions and conditions describedherein may be altered for compatibility with specific cell and specimentypes while still achieving the same or similar results as describedherein. All such similar substitutes and modifications apparent to thoseskilled in the art are deemed to be within the scope and spirit of theinvention as defined by the appended claims.

1-23. (canceled)
 24. A method for isolating CD36+ fetal cells from abiological fluid comprising the steps of: (a) isolating CD34+ cells fromthe biological fluid; (b) stimulating the isolated CD34+ cells toexpress CD36; (c) separating fetal cells from the non-fetal cellspresent in the isolated cells by contacting the isolated cells with oneor a plurality of antibodies that specifically bind to a cellularantigen that is detectably expressed by CD36+ fetal cells, but notdetectably expressed by CD36+ non-fetal cells; and (d) isolating CD36+fetal cells from step (c).
 25. The method of claim 24, wherein theantibody specifically binds to a cellular antigen identified as MS4A10,MS4A7, MS4A6A, ASGR2 or MS4A5.
 26. The method of claim 25, wherein theantibody specifically binds to SEQ ID NO:1, SEQ ID NO:2, SEQ ID NO:3,SEQ ID NO:4, SEQ ID NO:5, SEQ ID NO:6, SEQ ID NO:7, SEQ ID NO:8, SEQ IDNO:9 or SEQ ID NO:10.
 27. The method of claim 26, wherein the antibodyspecifically binds to SEQ ID NO:1.
 28. The method of claim 24, whereinthe CD34+ cells are incubated in the presence of the cytokines Flt-3ligand, TPO (thrombopoietin), and SCF (stem cell factor).
 29. The methodof claim 24, wherein the fetal cells are separated from the non-fetalcells by fluorescence activated cell sorting (FACS).
 30. The method ofclaim 24, wherein the fetal cells are separated from the non-fetal cellsby affinity chromatography.
 31. The method of claim 30, wherein theaffinity chromatography is performed by contacting the cells with theone or a plurality of the antibodies that are conjugated or bound to aninsoluble support.
 32. The method of claim 24, wherein the fetal cellsare separated from the non-fetal cells by magnetic separation.
 33. Themethod of claim 32, wherein magnetic separation is performed bycontacting the cells with the one or a plurality of the antibodies thatare conjugated or bound to a magnetic micro-particulate support.
 34. Themethod of claim 24, wherein the biological fluid is maternal peripheralblood.
 35. The method of claim 24, wherein the isolated CD34+ cells arestimulated to express CD36 in the presence of: (i) EPO (erythropoietin),SCF, Interleukin-3 (IL-3), and Interleukin-6 (IL-6); (ii) EPO, IGF-1(insulin-like growth factor-1), and SCF; or (iii) EPO, SCF, IL-3, andIGF-1.
 36. A method for detecting fetal cells in a biological fluidcomprising the steps of: (a) isolating CD34+ cells from the biologicalfluid; (b) stimulating the isolated CD34+ cells to express CD36; (c)binding or labeling the cells with one or a plurality of antibodies thatspecifically bind to a cellular antigen that is detectably expressed byCD36+ fetal cells, but not detectably expressed by CD36+ maternalperipheral blood cells; and (d) detecting the labeled fetal cells. 37.The method according to claim 36, wherein the biological fluid ismaternal peripheral blood.
 38. The method of claim 36, wherein the CD34+cells are incubated in the presence of the cytokines Flt-3 ligand, TPO(thrombopoietin), and SCF (stem cell factor).
 39. The method of claim36, wherein the isolated CD34+ cells are stimulated to express CD36 inthe presence of: (i) EPO (erythropoietin), SCF, Interleukin-3 (IL-3),and Interleukin-6 (IL-6); (ii) EPO, IGF-1 (insulin-like growthfactor-1), and SCF; or (iii) EPO, SCF, IL-3, and IGF-1.
 40. The methodof claim 36, wherein the fetal cells are detected by flow cytometry,microscopy or radiography.
 41. A method for detecting fetal cells in abiological fluid comprising: (a) isolating CD34+ cells from thebiological fluid; (b) labeling the isolated CD34+ cells by contactingthe cells with one or a plurality of detectably-labeled probes thatdetect expression of one or a plurality of genes that are AD026, AD037,AKNA, ASGR2, C1QG, CREM, CSPG2, CXCL16, DCNP1, GPR84, HRB2, JDP2, KCNJ2, MAFB, MGC21854, MRC1, MS4A4A, MS4A6A, MS4A7, MS4A10, MS4A5, NMES1,PAG, PARVG, PKIB, PRAM-1, PTGFRN, RASGRP4, RCP, S100A8, S100A9, or TIM3;and (c) detecting the labeled cells, wherein the detected labeled cellsare fetal cells.
 42. The method of claim 41, wherein thedetectably-labeled probe is an antibody that specifically binds to SEQID NO:1, SEQ ID NO:2, SEQ ID NO:3, SEQ ID NO:4, SEQ ID NO:5, SEQ IDNO:6, SEQ ID NO:7, SEQ ID NO:8, SEQ ID NO:9 or SEQ ID NO:10.
 43. Themethod of claim 42, wherein the detectably-labeled probe is an antibodythat specifically binds to SEQ ID NO:1.
 44. The method of claim 41,wherein the detectably-labeled probe is an mRNA probe or a riboprobe.45. The method of claim 41, wherein the biological fluid is maternalperipheral blood.
 46. The method of claim 41, wherein the CD34+ cellsare incubated in the presence of the cytokines Flt-3 ligand, TPO(thrombopoietin), and SCF (stem cell factor).
 47. The method of claim 41further comprising, following step (a), stimulating the isolated CD34+cells to express CD36.
 48. The method of claim 47, wherein the isolatedCD34+ cells are stimulated to express CD36 in the presence of: (i) EPO(erythropoietin), SCF, Interleukin-3 (IL-3), and Interleukin-6 (IL-6);(ii) EPO, IGF-1 (insulin-like growth factor-1), and SCF; or (iii) EPO,SCF, IL-3, and IGF-1.
 49. The method of claim 41, wherein the fetalcells are detected by flow cytometry, microscopy or radiography.
 50. Adiagnostic method wherein fetal cells obtained in accordance with claim24 are genetically evaluated using FISH, PCR or real time PCR.